There are a limited number of genetically defined animal models for atherosclerosis research available. In order to generate additional animal models, we will alter the normal metabolism in mice and rabbits either by overexpression or selective knockout of specific genes involved in lipoprotein metabolism or atherosclerosis. For knockout experiments, we have selected cholesterol 7alpha-hydroxylase and lipoprotein lipase. Cholesterol 7alpha-hydroxylase is a rate-limiting enzyme for bile acid biosynthesis from cholesterol. Knockout of this enzyme in mice would product an accumulation of cholesterol leading to elevated levels of plasma cholesterol. Lipoprotein lipase is a key enzyme in lipoprotein metabolism. Heterozygous lipoprotein lipase deficiency is a cause of familial combined hyperlipidemia in humans. We plan to reproduce this defect in mice by gene targeting. For overexpression, we have selected 15-lipoxygenase, scavenger receptor and HMGCoA reductase. 15- lipoxygenase appears to be important for the generation of oxidized low density lipoproteins, which are more atherogenic than the unoxidized form. These oxidized lipoproteins are taken up by the scavenger receptor on macrophages. Overexpression of 15-lipoxygenase and scavenger receptor, either individually or in combination, produces an animal that is much more susceptible to mild elevations of serum cholesterol. Overexpression of HMGCoA reductase causes the overproduction of cholesterol intracellularly and its secretion in the form of lipoproteins into the circulation. The overexpression experiments will be performed by microinjecting carefully designed transgenes into rabbits; mice will be used initially for testing the individual constructs. Our comprehensive approach should allow us to develop exciting new animal models for atherosclerosis research.